镨基复合金属氧化物负载的纳米金催化剂的制备及其构效关系研究

Oxygen vacancies on the surface of metal oxides usually works as the most reactive sites and play an important role in catalysis reaction. The controllable modulation of oxygen vacancies in metal oxides is one of the demanding points in catalyst preparation. One of the solutions would be using dopant, as by adding a second metal forming mixed oxide. Currently, lots of studies point that oxygen vacancies in the supported nano-gold catalysts could effectively promote the low temperature water gas shift reaction (WGSR, CO + H2O → CO2 + H2), however, the fundamental understandings for this effect is still ambiguous. Praseodymium-based oxides as an oxygen-rich support for gold nano-particles could therefore worked as an ideal system for studying the working mechanisms of oxygen vacancies in WGSR. In this project a series of Pr-TiOx, Pr-CeOx mixed oxides with controllable size, morphology and binding mode will be synthesized, which will then be used as supports to prepare supported nano-gold catalysts. In order to understand the structure-performance relationships of praseodymium mixed oxides supported gold catalysts in WGSR, the activation and dissociation effect of oxygen vacancies for molecule water and the construction effect of oxygen vacancies for the catalyst structure were investigated, respectively. Based on the experimental results, the working mechanism of oxygen vacancies for WGSR will be elucidated. The results of this project can provide both important experimental evidence and theoretical guidance on extending the applications of praseodymium-based mixed oxides in heterogeneous catalysis.

金属氧化物表面的氧空位通常是活性最高的部分在催化反应中起着关键作用。 如何可控的调变氧化物中的氧空位是催化剂制备过程中的一个难点，其中一个途径是通过掺杂形成复合金属氧化物。研究表明，纳米金催化剂载体中的氧空位对催化低温水煤气变换反应有着直接的促进作用，但其作用机理尚不明确。氧化镨中含有较多的氧空位，其相应的负载型金催化剂可以作为一个理想的体系来研究氧空位在水煤气变换反应中的作用机理。本项目中拟设计合成系列尺寸，形貌，结合方式可控的氧化镨-氧化钛，氧化镨-氧化铈的复合金属氧化物，以其作为载体，制备相应的负载型金催化剂。通过研究此类催化剂在水煤气变换反应中的催化行为，考察载体表面和体相中的氧空位对金的价态，稳定性以及水分子活化和解离的影响。揭示镨基复合金属氧化物负载的纳米金催化剂的结构特点与催化性能之间的内在联系。为探索和扩展镨基复合金属氧化物在多相催化领域中的应用提供理论和实验基础。

本项目围绕镨基复合氧化物负载纳米金催化剂的制备及其活性位点调控开展研究，以期揭示催化剂的结构（形貌，组成）特点与催化性能之间的内在联系问题。通过对氧化物载体的形貌（棒状）和组成（Pr : Ce, Pr : Ti）调控、金负载方式的优化（改性的沉积沉淀法）等，最终获得高活性高稳定的纳米金催化剂。 研究发现直接利用氢氧化物载金可以制备出金纳米粒子更加分散的催化剂，主要是由于载体表面丰富的氢氧根基团和氧空位可以起到很好的锚定金纳米粒子的作用。 利用水热法和溶胶凝胶法可以分别合成棒状和纳米片状复合氧化物载体。通过调变复合氧化物中元素比例可以调变氧空位的浓度和化学环境，同时也可调变纳米金的化学价态。两种方法制备的Au/CeaPrbOx，Au/TiaPrbOx在特定混合比例下在水煤气变换反应中都显示了较高活性和稳定性。 对于材料的表征和催化反应机理的解析为后续开展镨基复合氧化物负载的纳米金催化剂的进一步开发和利用提供了很好的实验基础和理论指导。